Hexavalent chromium, or Cr(VI), is among the most widespread contaminants in water resources in the U.S. and around the world. Cr(VI) has been found in at least 1,127 of the 1,699 current or former National Priority List (NPL) sites, which have been identified by the U.S. Environmental Protection Agency (EPA) as the most serious hazardous waste sites in the nation and are the highest priority targets for long-term federal cleanup activities. Toxicological research has found that high concentrations of Cr(VI) can contribute to stomach cancers, kidney and liver damage, and reproductive harm. As a result, there is significant demand among water providers and managers of Superfund sites for innovative technologies to address Cr(VI) contamination in a cost-effective and environmentally sustainable manner. The lack of cost-effective technologies to reduce Cr(VI) levels in water are due to technical challenges associated with existing physical/chemical approaches, including high cost, the need for disposal of secondary waste streams, and performance that can be vulnerable to influent water geochemistry. Specifically, there is a need for new technologies to reliably reduce Cr(VI) to very low parts-per-billion levels with lower costs and less waste than existing physical or chemical treatment technologies. This project seeks to address this need through a novel combination of materials science and bacterial reductive immobilization. In contrast to conventional physical or chemical technologies, this new technology does not produce a hazardous secondary waste stream. Moreover, the proposed technology offers unique redox flexibility, which allows it to remain effective even while hydrogeological characteristics may change. These and other advantages help position the proposed technology as a highly effective ex-situ or in-situ treatment approach to achieve low concentrations of Cr(VI) in water. In the proposed project, a prototype of the proposed technology is developed through comprehensive kinetic studies under various operating conditions supported by whole-genome transcriptional studies. In addition to developing optimum parameters for the treatment system, the project will also provide insights into the unique physiology employed to achieve reductive immobilization of Cr(VI). Development of material composites to deploy a high density of the targeted culture proceeds in an iterative manner to ultimately select one composite to evaluate in a continuous-flow reactor study using both synthetic and actual contaminated groundwater. The outcome of this project will be the proof-of-concept of a new technology for efficient, environmentally friendly, and cost-effective Cr(VI) treatment. As a result, this project holds significant promise to provide a critically necessary tool for protecting and remediating drinking water supplies from chromium contamination, thus promoting public safety and environmental health.